Though tec is right, I'd like to clarify. because your fish is in another tank, you could cure your LR right in your new 55gal.

You can use a turkey baster or a siphon to clean the bottom of the tank. your 10g will make a nice quarantine tank once you take the LR out of it. (this is because you may need to medicate a QT, and LR will be damaged by this)

I agree that you should look for another LFS too. If you keep testing, and keep up with WC's you can keep this fish alive while you get your 55 up to speed. don't rush the 55. you will need to be sure the cycle is done before moving your fish.